(1) Field of the Invention
The present invention relates to the field of aircraft fuselages made up mainly of stiffener members for stiffening a covering that defines the volume of the fuselage. The present invention relates more particularly to the structural arrangement of such a fuselage for a rotorcraft, and still more particularly to the mutual arrangement of fuselage members that are mechanically load-bearing relative to the general forces to which the fuselage is subjected.
In the field of aviation, aircraft fuselage structures comprise stiffener members constituted essentially firstly by longitudinal stiffeners for stiffening walls formed by a covering, and secondly by transverse stiffeners.
(2) Description of Related Art
For a so-called “multi-stringer shell” fuselage structure, the longitudinal stiffeners comprise longerons and bent or extruded section members, commonly referred to as stringers, that are fastened to the covering. Under such circumstances, the walls transmit all of the general forces supported by the fuselage to the fuselage structure, in particular in bending and in twisting.
The transverse stiffeners essentially comprise shaper frames, commonly referred to as strong frames, that are arranged in register with zones where forces are applied to the fuselage structure. Such frames, which may be individually of structures and shapes that are similar or distinct, are typically arranged in succession, being spaced apart from one another in the longitudinal direction of the fuselage between the front and the rear of the aircraft.
Furthermore, the frames are used for organizing the inside of the fuselage by providing supports for partitioning structures, such as vertical partitions or horizontal equipment floors. The inside volume of the fuselage is thus subdivided into a plurality of compartments providing cabin space functions or equipment space functions. Such partitioning structures serve essentially to support localized forces that are specific to their functions and they are commonly considered as being structures that are not load-bearing with respect to the general forces to which the fuselage is subjected.
In this context, the way in which the structure of the fuselage of an aircraft is arranged is closely associated with the type of aircraft, in particular with whether it is an airplane or a rotorcraft. Specifically, the fuselage structure needs to take account of the general forces to which the fuselage of an aircraft of a given type is typically subjected and also of the kinds of mission flown by that aircraft, which together determine the way in which the fuselage is arranged and the way in which the compartments subdividing its inside volume are organized.
For rotorcraft, the general forces to which the fuselage is subjected are generated essentially:
by one or more rotors or indeed by one or more propulsive propellers of the rotorcraft that provide it with lift, guidance, and propulsion in any travel direction. A rotorcraft typically has at least one main rotor of substantially vertical axis that provides the rotorcraft at least with lift and propulsion. The attitude in flight of the rotorcraft can be modified by the pilot acting on cyclic and/or collective variation of the pitch of the blades making up the rotary wing of the main rotor. Rotorcraft are also provided with an anti-torque device mounted at the end of a tail bottom and serving to guide the rotorcraft in yaw. Conventionally, but not exclusively, such an anti-torque device is constituted for example by a tail rotor having a substantially horizontal axis;
by one or more undercarriages forming interfaces between the rotorcraft and the ground, such as an undercarriage having wheels or skids. Such undercarriages generate general forces that are supported by the fuselage when the rotorcraft makes contact with the ground;
by transporting heavy loads, where “heavy” is conventionally considered as weighing more than 300 kilograms (kg) and may be as much as several (metric) tonnes. Such heavy loads, which are typically transported using slings, are conventionally distinguished from other loads that are considered as being light. As an indication, such “light” loads may for example relate to transporting freight by winching and/or in a hold, and may relate to various pieces of lightweight equipment on board the aircraft, or indeed to people being transported; and
by carrying heavy equipment of the rotorcraft, such as fuel tanks and/or a power plant providing the mechanical power needed to operate the rotorcraft, and in particular to drive its rotor(s).
Under such conditions, the main rotor(s) and the power plant are mounted on the fuselage via a load-bearing top floor secured to at least two transverse frames defining a middle segment of the fuselage. Such a middle segment is interposed in particular between a cockpit and the tail boom carrying the anti-torque device. By way of example, reference may be made on this topic to Document US 2006/0243854 (Sikorsky Aircraft Corp.), which describes ways of mounting a rotorcraft main rotor on such a load-bearing top floor.
Undercarriages are conventionally connected to load-bearing members of the fuselage, in particular members engaging at least one transverse frame. By way of example, reference may be made to Document FR 2 895 369 (Eurocopter France), which describes ways of mounting skid landing gear to a rotorcraft fuselage.
For transporting heavy loads, sling equipment is commonly mounted on at least one load-bearing member of the fuselage, while ensuring that the axis on which heavy loads are carried by means of a sling is substantially in alignment with the axis of the main rotor in order to avoid destabilizing the rotorcraft. Sling equipment may potentially be installed under the fuselage or it may be carried by the top floor and then extend towards the ground, in particular after passing vertically through the inside volume of the fuselage. By way of example, reference may be made on this topic to Document FR 2 970 944 (Eurocopter France) which describes such sling equipment mounted on board a rotorcraft.
Fuel tanks may possibly be received in a bottom zone of the fuselage, commonly referred to as its bottom section, the fuel tanks resting on the bottom wall or belly constituting the bottom of the bottom section of the fuselage. The belly of the fuselage, which is subjected to the forces generated by the weight of the on-board fuel, is held in shape by means of the covering and by means of the longitudinal stiffeners of the fuselage that engage the bottom edges of the frames. By way of example, reference may be made on this topic to Documents FR 2 756 255 (Eurocopter France) and EP 2 567 896 (Eurocopter France), which describe ways of installing fuel tanks in compartments arranged in the substructure of a rotorcraft fuselage.
Fuel tanks may also be installed inside a compartment inside the fuselage and secured to the top floor and/or to at least one transverse frame of the fuselage. By way of example, reference may be made on this topic to Document U.S. Pat. No. 5,451,015 (Bell Helicopter Textron Inc.), which describes such ways of installing a fuel tank on board a rotorcraft behind a cockpit.
Auxiliary or main fuel tanks may also be installed laterally on the rotorcraft, being carried by at least one transverse frame of the fuselage and/or by at least one beam of the fuselage. By way of example, reference may be made on this topic to Documents U.S. Pat. No. 4,860,972 (ERA Aviat. Inc.) and U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.).
Furthermore, concerning the internal organization of the fuselage, a cabin space of the rotorcraft is conventionally organized as a front cockpit and at least one middle cabin space arranged between the cockpit and the tail boom. Vertical partitions subdivide the cabin space longitudinally and/or transversely, said partitions being supported directly or indirectly by the transverse frames of the fuselage. Such vertical partitions serve to provide various spaces inside the fuselage of the rotorcraft, such as at least one cabin space or at least one equipment space.
The fuselage is also conventionally subdivided by a horizontal equipment floor separating the cabin space from the bottom section. The cabin space is arranged above the bottom section, with at least one cabin space if not also the cockpit overlying one or more compartments in the bottom section providing a hold or housing fuel tanks.
The available space in the bottom section may also be potentially used for housing electrical cables, hydraulic or airflow ducts, or indeed linkages for transmitting flight commands, for example. Such electrical cables, hydraulic or airflow ducts, and/or linkages extending on board the aircraft are referred to below as “long members”. The bottom section may also possibly be used for providing an equipment space housing equipment of the rotorcraft, and/or a hold.
By way of example, reference may be made on this topic of the internal arrangement of a rotorcraft fuselage to Document EP 0 581 626 (Eurocopter France).
With reference to the equipment floors that separate the cabin space from the bottom section, reference may be made to Document FR 2 974 754 (Daher Aerospace), which describes an embodiment of a composite panel used for forming an equipment floor for aircraft.
Reference may also be made to Documents FR 2 939 404 (Airbus France SA) and FR 2 939 405 (Airbus France SA), which describe ways of mounting such panels on board an aircraft in order to form an equipment floor. Equipment floors are commonly fastened to load-bearing members, such as beams, cross-members, and/or support legs, which members are mounted on the fuselage. By way of example, reference may be made to Documents FR 2 933 065 (Airbus France SAS), FR 2 957 050 (EADS France), FR 2 984 273 (Aerolia SAS), and FR 2 947 524 (Airbus Operations SAS), which describe various ways of mounting an equipment floor on board an aircraft.
When considering the structural arrangement of the fuselage, it is necessary to take account of the fact that the internal organization of the fuselage must be adaptable to the various flight missions that the rotorcraft might be required to undertake.
For example, it is necessary to take account of the wide variety of flight missions relating to transporting passengers in the cabin space, while allowing for different comfort thresholds depending on the quality and/or the function of the passengers on board. Also by way of example, specific flight missions relate to transporting light loads, such as transporting freight and/or to carrying specific pieces of equipment in the cabin space.
More particularly, such light loads that are transported may be located inside a compartment of the fuselage, such as in a hold or in a cabin space of the rotorcraft. Light loads may also be transported and/or moved between the outside and the inside of the fuselage by winching. Light loads are conventionally transported by winching performed by means of a winch carried by a fuselage member having the winch fastened thereto either directly or indirectly.
In the context of equipment floors forming loading planes that are fitted out beforehand depending on given flight missions, such planes are arranged in a variety of configurations depending on the specific flight missions of the rotorcraft. For example, equipment floors may be fitted out beforehand with a variety of fastener members for anchoring seats and/or freight, in particular, or indeed for anchoring various cords.
It can be understood that for a given flight mission of a rotorcraft, the equipment floor of the rotorcraft needs to be fitted out beforehand, e.g. for transporting a predefined number of passengers that might be variable, under comfort conditions and equipment conditions that vary depending on the quality and/or the on-board function of the passengers. The equipment floor may also be arranged specifically for transporting freight. By way of example, reference may be made on this topic to Documents U.S. Pat. No. 5,517,895 (Sanderson, P. H.), FR 2 953 485 (Airbus Operations SAS), and FR 2 947 527 (Airbus Operations).
Furthermore, equipment floors commonly include channels for passing electric cables for electrically powering equipment carried in the cabin either permanently or specifically for a given flight mission, or indeed for providing specific electrical power supply outlets that are suitable for use by passengers depending on their quality and/or their function on board the aircraft.
The variety of flight missions makes it difficult to use the same equipment floor for all potential flight missions of a rotorcraft. Therefore a variety of equipment floors that are specifically fitted out for respective flight missions are used as alternatives. By way of example, reference may be made on this topic to Document FR 2 960 514 (Airbus Operations).
Furthermore, having the equipment floor overlying the bottom section constituting the equipment space means that the equipment floor needs to be organized specifically to give an operator access to the volume inside the bottom section. For this purpose, hatches giving access to the bottom section are arranged and distributed in a variety of ways in such equipment floors. Nevertheless, accessing the bottom section is difficult, as mentioned in Documents U.S. Pat. No. 5,371,935 (United Tech. Corp.) and U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.), which propose overcoming such difficulties of accessing fuel tanks housed in specific compartments of the fuselage.
Consequently, it can be seen that the overall arrangement of a fuselage needs to take account of it being necessary for a variety of technical floors to be interchangeable quickly and easily. Specifically, it is appropriate for the way the fuselage is arranged to make it easy and quick to replace various equipment floors fitted out in specific ways, while also providing the facility of accessing the volume inside the bottom section that may house fuel tanks or any other equipment carried in the belly of the rotorcraft.
Furthermore, when designing the structure of the fuselage and the way it is organized externally, account must be taken of a situation in which the rotorcraft crashes. More particularly, the strength of the fuselage, and the way in which various pieces of equipment are installed on the fuselage needs to be taken into account in order to achieve good security for people in the event of the rotorcraft crashing.
In the context of an aircraft fuselage, the concepts of “load-bearing” and “non-load-bearing” are concepts commonly used by the person skilled in the art for describing members, where such concepts relate to whether fuselage members are or are not load-bearing relative to the general forces supported by the fuselage.
It should also naturally be understood that the concepts of “vertical”, “horizontal”, “longitudinal”, “transverse”, “front”, “rear”, “bottom”, “top”, and “overlying” are concepts that are relative and that need to be assessed relative to the situation of the rotorcraft when standing on the ground, and relative to the longitudinal extent of the fuselage between the front and the rear of the rotorcraft. Such concepts are commonly used by the person skilled in the art.
For knowledge of a technical background remote from the present invention but relating to fuselage structures for a rotorcraft, reference may also be made to Documents FR 1 530 625 (Boeing Co.), DE 10 2006 019220 (Hochschule für Angewandte), US 2009/146010 (Nehemia Cohen), DE 199 24 480 (Uti Holding & Man Ag), and also the document “Boeing Vertol Chinook HC Mk1”, Pilot Press (Dec. 1, 2012) taken from the Internet on Jul. 7, 2014 at the following URL address: http://sobchak.files.wordpress.com/2009/08/ch47cut.gif
In this context, it can be seen that structuring the fuselage of a rotorcraft involves continuous research on the part of the person skilled in the art confronted with a multitude of problems to be solved and difficulties to be overcome.
Solutions need to be found for achieving a satisfactory compromise between the various drawbacks and advantages associated with such solutions, often depending on the selections made by designers depending on their perceptions of the problems to be solved and the difficulties to be overcome.